Silicate urolithiasis in a paediatric patient.

Silicate urolithiasis is rare in humans (0.2%) but common in herbivorous animals. We report a previously unreported instance in India where a pediatric patient with renal pelvic calculus who underwent percutaneous nephrolithotomy was found to have silicate urolithiasis on stone analysis. Retrospective analysis did not reveal any risk factors associated with silicate stone formation.

INTRODUCTION

Paediatric urolithiasis constitutes about 4.3% of all the cases.[1] In humans, silicate urolithiasis incidence is very rare (0.2%) but common in herbivorous animals. It is usually reported in a patient with excess ingestion of silicates in the form of magnesium trisilicate as antacid for peptic ulcer disease for long term. We report a case of pediatric silicate urolithiasis without a history of magnesium trisilicate or other risk factors. This case is unique in that it is the first reported case of silicate urolithiasis in India.

CASE REPORT

An 8-year-old female child presented with left flank pain of 6 months duration. On evaluation, she was found to have a left renal pelvic calculus of 11 mm (465 HU) with mild hydronephrosis [Figure 1]. Urine analysis revealed a pH of 7.0 and the examination of urinary sediment showed 8–10 pus cells and 1–2 red blood cells per HPF. Peripheral blood count and blood biochemistry were unremarkable. Urine culture was sterile. She underwent left percutaneous nephrolithotomy (PCNL) with a tract size of 24 Fr. Postoperative period was uneventful. Physical appearance of the stone was yellowish brown. On stone analysis by infrared spectrophotometry [Figure 2], it was identified as a silicate stone (Alpha-Quartz, silicon dioxide). Retrospective analysis revealed no history of excess ingestion of silicate, typically in the form of antacid intake or other risk factors. On 1-year follow-up, there was no recurrence. Metabolic workup was normal.

Figure 1

Noncontrast computed tomography showing left renal pelvic calculus (arrow)

Figure 2

On infrared spectrophotometry, its wavelength exhibits a peak at 1100 cm−1 suggesting its major composition as silicon dioxide

DISCUSSION

Pediatric urolithiasis comprises about 4.3% of all the cases. Apart from malnutrition, high salinity and warm temperature are contributing factors to the prevalence of urolithiasis.

Silicate stones are extremely rare type of urolithiasis, with incidence of 0.2% in humans.[2] In Japan, urinary silicate calculi have been reported in fifty patients.[3] Most of the patients were in the age group 24 and 77 years, except a 10-month-old infant. It is usually associated with consumption of a large amount of silicate containing antacids such as magnesium trisilicate.[4] Other risk factors for silicate stone are malnutrition, infection, diet poor in proteins, drugs such as zonisamide (antiepileptic). Our case had no history of any excess ingestion of silicates in the form of antacids, etc. Only two cases without magnesium trisilicate intake have been reported.[3]

The proposed mechanism of silicate stone formation is urinary alkalinization and high concentration of silica in the urine. Takemoto, assumed that high urinary concentration of silicates induces aggregation, followed by deposition of calcium salts around silicate gel.[5] The 24-h urinary levels of silicate were not measured in this patient, which is a limitation in our case. On urine analysis, silicate crystals look like round to oval to rhomboid crystals under microscope, but it should be confirmed under infrared. On infrared spectrophotometry, its wavelength exhibits a peak at 1100 cm-1, which indicates that the major composition (98%) is silicon dioxide. Management of urolithiasis in children requires complete clearance, eradication of urinary tract infection, and correction of any metabolic or anatomical abnormalities.

The treatment options are shockwave lithotripsy, PCNL, retrograde intrarenal surgery. PCNL is a well-accepted procedure in children as well as in adults. Ganpule et al. stated that PCNL offers good clearance rates with acceptable morbidity.[1] In our case, we achieved complete stone clearance with PCNL and follow-up for 1 year showed no recurrence.

In summary, concerning our case, there were no associated risk factors for silicate stone in any form. Although silicate stones are rare, it should be considered while doing metabolic workup. To the best of our knowledge, this is the first reported case of silicate urolithiasis in India.